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Dec 2012

Volume 50, Issue 9, pp. 516-575

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Smashing pumpkins

Frank Lock

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 516

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01.50.My Demonstration experiments and apparatus
07.10.-h Mechanical instruments and equipment

Explaining Monty Hall

Elena Kuchina

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 516

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01.55.+b General physics
02.50.Le Decision theory and game theory

Author's response

Edwin A. Karlow

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 516

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01.50.-i Educational aids
02.50.Cw Probability theory
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CONE, BALL, AND CUP

Paul Hewitt

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 518

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01.50.Kw Techniques of testing
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Astrophotography on the Cheap

Chuck Niederriter and Mario Belloni

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 520

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Teaching introductory astronomy means discussing celestial objects that are beyond most students' experience. Simply talking about them is usually not sufficient to convey their size, distance, complexity, and beauty.2 One way that we introduce our students to celestial objects is through observing sessions,3,4 but we have also extended these observing sessions to include astrophotography (AP). This approach relies on recent advances in the field of astrophotography. New computerized tracking and autoguiding mounts and digital still and video photography have made it easier5,6 and cheaper to take high-quality astrophotographs. While it is easy to spend $15,000 or more on a single astrophotography setup or even a single device (telescope, camera, and mount), taking simple, short-exposure photos can cost anywhere from $50 to a few hundred dollars depending on how much equipment you already have.
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01.50.Pa Laboratory experiments and apparatus
07.68.+m Photography, photographic instruments; xerography
95.75.De Photography and photometry (including microlensing techniques)

Imaging Emission Spectra with Handheld and Cellphone Cameras

David Sitar

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 524

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As point-and-shoot digital camera technology advances it is becoming easier to image spectra in a laboralory setting on a shoestring budget and get immediale results. With this in mind, I wanted to test three cameras to see how their results would differ. Two undergraduate physics students and I used one handheld 7.1 megapixel (MP) digital Cannon point-and-shoot auto focusing camera and two different cellphone cameras: one at 6.1 MP and the other at 5.1 MP.
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01.50.-i Educational aids
07.68.+m Photography, photographic instruments; xerography
32.50.+d Fluorescence, phosphorescence (including quenching)
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Elastic Properties of Plasticine, Silly Putty, and Tennis Strings

Rod Cross

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 527

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How would a physicist describe the elastic properties of an apple or a banana? Physics students and teachers are familiar with the elastic properties of metal springs, but are likely to be less familiar with the elastic properties of other common materials. The behavior of a metal spring is commonly examined in the laboratory by adding masses to measure the change in the extension or compression. A banana or an apple or any other relatively soft material could just as easily be examined in the same way, as an additional and entertaining exercise. Even if an apparatus is not readily available to undertake such an experiment, it can easily be constructed.1,2 In this article I compare the elastic properties of Plasticine (a brand of modeling clay), Silly Putty, and tennis strings. All three materials behave in the same qualitative manner when stretched or compressed slowly, despite the fact that they are quite different when stretched or compressed rapidly and despite the fact that Plasticine and Silly Putty are both much softer than a tennis string. Typical results for a slow deformation are shown in Fig. 1.
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01.50.My Demonstration experiments and apparatus
62.20.D- Elasticity
62.20.F- Deformation and plasticity
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Another “Find-the-Flaw” Test

Göran Grimvall

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 530

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Daniel F. Styer1 recently discussed physics problems where several different algebraic results are presented, and the task is to identify the correct result through reasoning based on a general understanding of physics principles. Here is a related, but more general, problem. A graph with several quite disparate captions is presented (Fig. 1). The task is to find the only caption that could be correct.
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01.50.F- Audio and visual aids
01.50.Kw Techniques of testing
02.10.-v Logic, set theory, and algebra

Data Acquisition Using Xbox Kinect Sensor

Jorge Ballester and Charles B. Pheatt

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 531

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The study of motion is central in physics education and has taken many forms as technology has provided numerous methods to acquire data. For example, the analysis of still or moving images is particularly effective in discussions of two-dimensional motion. Introductory laboratory measurement methods have progressed through water clocks, spark timers, stopwatches, Polaroid cameras, videocassette recorders, ultrasonic devices, digital video, and most recently high-speed digital video.1 In this paper we explore the use of newly available imaging technology for the study of motion. The Kinect sensor was introduced in November 2010 by Microsoft as an accessory for the Xbox 360 video game system. Shortly after the product release, a software framework became available that allows a personal computer to capture output from a stand-alone Kinect.2 Author-developed data acquisition software for the Kinect and several experimental examples are discussed.
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01.50.-i Educational aids
45.40.Gj Ballistics (projectiles; rockets)

Another Look at Rocket Thrust

Brooke Hester and Jennifer Burris

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 534

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Rocket propulsion is often introduced as an example of Newton's third law. The rocket exerts a force on the exhaust gas being ejected; the gas exerts an equal and opposite force—the thrust—on the rocket.1,2 Equivalently, in the absence of a net external force, the total momentum of the system, rocket plus ejected gas, remains constant. The law of conservation of momentum is generally used in textbooks3,4 and elsewhere5 in deriving the rocket thrust equation. In this paper we take the somewhat different approach of explicitly applying Newton's second law to the rocket. This method provides a good opportunity to show the importance of choosing carefully the system to which Newton's second law is applied.
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01.50.My Demonstration experiments and apparatus
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

The Electric Whirl in the 19th and 21st Centuries

John A. Daffron and Thomas B. Greenslade, Jr.

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 536

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The electric whirl or electric fly in Fig. 1 is one of the many electrostatic demonstrations from the 19th century that continue to amuse and delight students today.1 It also introduces them to some good physics.
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01.50.My Demonstration experiments and apparatus
47.00.00 Fluid dynamics
62.10.+s Mechanical properties of liquids

A Simple Apparatus for Demonstrating Fluid Forces and Newton's Third Law

Pirooz Mohazzabi and Mark C. James

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 537

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Over 2200 years ago, in order to determine the purity of a golden crown of the king of Syracuse, Archimedes submerged the crown in water and determined its volume by measuring the volume of the displaced water.1 This simple experiment became the foundation of what eventually became known as Archimedes' principle: An object fully or partially immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object. The principle is used to explain all questions regarding buoyancy, and the method is still prescribed for determination of the volume of irregularly shaped objects.2
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01.40.gb Teaching methods and strategies

Want to Reduce Guessing and Cheating While Making Students Happier? Give More Exams!

James T. Laverty, Wolfgang Bauer, Gerd Kortemeyer, and Gary Westfall

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 540

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It is almost universally agreed that more frequent formative assessment (homework, clicker questions, practice tests, etc.) leads to better student performance and generally better course evaluations.1 There is, however, only anecdotal evidence that the same would be true for more frequent summative assessment (exams). There maybe many arguments against giving more exams, including the general “pain” associated with examinations, as well as reduced teaching time, since classroom sessions are dedicated to exams rather than lecturing. We present evidence that increasing the number of exams in fact does lead to better learning success, less cheating and guessing on homework, and better student course evaluations.
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01.50.My Demonstration experiments and apparatus
42.79.Pw Imaging detectors and sensors
01.50.ht Instructional computer use

Neutrons as Party Animals: An Analogy for Understanding Heavy-Element Fissility

B. Cameron Reed

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 544

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I teach a general education class on the history of nuclear physics and the Manhattan Project. About halfway through the course we come to the discovery of fission and Niels Bohr's insight that it is the rare isotope of uranium, U-235, which fissions under slow-neutron bombardment as opposed to the much more common U-238 isotope. As an “explanation” of the differing responses of the two isotopes to bombarding neutrons, I use the known (measured) masses of the various isotopes involved to compute the energies released upon neutron capture and then compare them to the fission barriers of the “compound” nuclei so formed (U-236 and U-239). The energy released in the (neutron + U-235) reaction exceeds the fission barrier by about one million electron-volts (1 MeV), while that for the (neutron + U-238) case falls about 1.6 MeV short. (The fission barriers are respectively about 5.7 and 6.5 MeV.)
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01.50.-i Educational aids
25.40.-h Nucleon-induced reactions
25.85.Ec Neutron-induced fission

Exploring Uncertainty with Projectile Launchers

Chad Orzel, Gary Reich, and Jonathan Marr

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 546

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The proper choice of a measurement technique that minimizes systematic and random uncertainty is an essential part of experimental physics. These issues are difficult to teach in the introductory laboratory, though. Because most experiments involve only a single measurement technique, students are often unable to make a clear distinction between random and systematic uncertainties, or to compare the uncertainties associated with different techniques. In this paper, we describe an experiment suitable for an introductory college-level (or advanced high school) course that uses velocity measurements to clearly show students the effects of both random and systematic uncertainties.
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01.50.My Demonstration experiments and apparatus
06.30.Gv Velocity, acceleration, and rotation
45.40.Gj Ballistics (projectiles; rockets)
01.40.ek Secondary school

Frames of Reference in the Classroom

Joshua Grossman

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 548

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The classic film “Frames of Reference”1,2 effectively illustrates concepts involved with inertial and non-inertial reference frames. In it, Donald G. Ivey and Patterson Hume use the cameras perspective to allow the viewer to see motion in reference frames translating with a constant velocity, translating while accelerating, and rotating—all with respect to the Earth frame. The film is a classic for good reason, but today it does have a couple of drawbacks: 1) The film by nature only accommodates passive learning. It does not give students the opportunity to try any of the experiments themselves. 2) The dated style of the 50-year-old film can distract students from the physics content. I present here a simple setup that can recreate many of the movies demonstrations in the classroom. The demonstrations can be used to supplement the movie or in its place, if desired. All of the materials except perhaps the inexpensive web camera should likely be available already in most teaching laboratories. Unlike previously described activities, these experiments do not require travel to another location3 or an involved setup.4,5
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01.50.My Demonstration experiments and apparatus
01.50.ff Films; electronic video devices

The Period of a Swinging Rod in an Oscillating Frame of Reference

Hubert Biezeveld

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 550

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It was obvious long ago that for mechanical behavior a gravitational field and an accelerating frame of reference are equivalent.1 Or in other words: it is impossible to decide whether you are in an accelerating elevator or in a closed room on a planet with a different value of g. In the first section of this article I will describe a simple experiment that illustrates this. In the second part I will give a numerical model that predicts the results. Data collection and the calculations were carried out using Coach and CoachLab2.2
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01.50.My Demonstration experiments and apparatus
46.70.Hg Membranes, rods, and strings

Rainbow Near Midday

David A. Cornell

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 552

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It was near midday on Sunday, Sept. 25, 2011. My family and I were coming home in the car when we saw strongly colored bands in the sky near the northern horizon. The effect was striking and attracted motorists to stop and gaze at it. Houses in the north seemed to be wearing a gently curving band of colors above the roof. If this were a rainbow, it was like no other that I had seen before. I quickly ran to get a camera to capture the effect before it vanished. See Fig. 1 for an image of the phenomenon.
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01.50.-i Educational aids

A Mass Spectrometer Simulator in Your Computer

Michel Gagnon

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 553

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Introduced to study components of ionized gas, the mass spectrometer has evolved into a highly accurate device now used in many undergraduate and research laboratories.1 Unfortunately, despite their importance in the formation of future scientists, mass spectrometers remain beyond the financial reach of many high schools and colleges. As a result, it is not possible for instructors to take full advantage of this equipment. Therefore, to facilitate accessibility to this tool, we have developed a realistic computer-based simulator. Using this software, students are able to practice their ability to identify the components of the original gas, thereby gaining a better understanding of the underlying physical laws. The software is available as a free download.
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01.50.ht Instructional computer use
07.75.+h Mass spectrometers
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Teaching the Concept of Resonance with the Help of a Classical Guitar

M. Kaan Kasar, Kemal Yurumezoglu, and Serap Kaya Sengoren

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 558

Online Publication Date: Nov 2012

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Resonance refers to the vibrations of larger amplitude that are produced under the effect of a harmonic driving force.1 Although resonance is an essential concept behind many events happening in nature, students usually have difficulty in learning and explaining the phenomenon. Various demonstrations are carried out in physics classes to clarify the concept of resonance.2–6
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01.50.My Demonstration experiments and apparatus
43.20.Ks Standing waves, resonance, normal modes
43.75.Gh Plucked string instruments
46.40.Ff Resonance, damping, and dynamic stability

Cooling Rates of Humans in Air and in Water: An Experiment

Craig F. Bohren

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 560

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In a previous article1 I analyzed in detail the physical factors resulting in greater cooling rates of objects in still water than in still air, emphasizing cooling of the human body. By cooling rate I mean the rate of decrease of core temperature uncompensated by metabolism. I concluded that the “correct ratio for humans is closer to 2 than to 10.” To support this assertion I subsequently did experiments, which I report following a digression on hypothermia.
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01.50.Pa Laboratory experiments and apparatus
87.19.Pp Biothermics and thermal processes in biology

Advanced Imaging of Elementary Circuits

William H. Baird, Caleb Richards, and Pranav Godbole

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 561

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Students commonly find the second semester of introductory physics to be more challenging than the first, probably due to the mechanical intuition we acquire just by moving around. For most students, there is no similar comfort with electricity or magnetism. In an effort to combat this confusion, we decided to examine simple electric circuits with either a high-speed camera or a thermal imager in an effort to make things like current and voltage as familiar as slow motion or temperature.
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01.50.My Demonstration experiments and apparatus

Determining Atmospheric Pressure Using a Water Barometer

C. Frederick Lohrengel, II and Paul R. Larson

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 563

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The atmosphere is an envelope of compressible gases that surrounds Earth. Because of its compressibility and nonuniform heating by the Sun, it is in constant motion. The atmosphere exerts pressure on Earth's surface, but that pressure is in constant flux. This experiment allows students to directly measure atmospheric pressure by measuring the mass of the water that is used as the fluid medium in the barometer. Simple calculations based upon the mass of water collected from the barometer yield the mass of the atmosphere per square unit of area at the site where the experiment is conducted.
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01.50.Pa Laboratory experiments and apparatus
92.60.hv Pressure, density, and temperature

Teachers' approaches to teaching physics

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 565

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Benjamin Franklin said, “Tell me, and I forget. Teach me, and I remember. Involve me, and I learn.” He would not be surprised to learn that research in physics pedagogy has consistently shown that the traditional lecture is the least effective teaching method for teaching physics. We asked high school physics teachers which teaching activities they used in their classrooms. While almost all teachers still lecture sometimes, two-thirds use something other than lecture most of the time. The five most often-used activities are shown in the table below. In the January issue, we will look at the 2013 Nationwide Survey of High School Physics teachers. Susan White is Research Manager in the Statistical Research Center at the American Institute of Physics; she directs the Nationwide Survey of High School Physics Teachers. If you have any questions, please contact Susan at swhite@aip.org.
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01.40.-d Education
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Smartphones—Experiments with an External Thermistor Circuit

Kyle Forinash and Raymond F. Wisman

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 566

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This contribution adds a further example to illustrate how to use the headphone port of a smartphone to receive data from an external circuit, in this case, a simple, adaptable homemade example for temperature measurement.1
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01.50.Pa Laboratory experiments and apparatus
07.20.Dt Thermometers
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
01.50.My Demonstration experiments and apparatus
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One Giant Leap

Boris Korsunsky, Column Editor

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 568

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Abstract Unavailable
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01.30.-y Physics literature and publications
01.50.Rt Physics tournaments and contests
45.05.+x General theory of classical mechanics of discrete systems
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A Physics Potpourri

Diane Riendeau, Column Editor

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 569

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This month's column consists of a mixture of short videos that can be used to liven up a classroom discussion.
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01.30.-y Physics literature and publications
01.50.ff Films; electronic video devices
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Fermi Questions

Larry Weinstein, Column Editor

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 569

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01.50.fh Posters, cartoons, art, etc.
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Squeezing light

Luka Vidic and Miha Kos

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 570

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01.50.My Demonstration experiments and apparatus
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Taking physics class into the world

Chris Chiaverina

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 572

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The world outside the classroom provides endless possibilities for discovering and understanding nature's laws. My colleague Jim Hicks and I have found that through experiments and exploratory activities performed in non-traditional settings, students can be made aware of the beauty and wonders of physics operating on a larger scale. Furthermore, such experiences make evident the examples and applications of physics in everyday life.
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01.50.My Demonstration experiments and apparatus
45.05.+x General theory of classical mechanics of discrete systems
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Physics of Breaking Bottles by Hand, preview, tinyurl.com/WSbottle; arxiv.org/abs/1210J764

Dan MacIsaac, Column Editor

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 574

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Abstract Unavailable
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01.30.-y Physics literature and publications
01.50.Rt Physics tournaments and contests
06.30.Gv Velocity, acceleration, and rotation

Super Ultimate Graphing Challenge kinematics graphing game by Matthew Blackman, theuniverseandmore.com

Dan MacIsaac, Column Editor

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 574

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Abstract Unavailable
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01.50.fh Posters, cartoons, art, etc.

Red Bull Stratos Jump analysis by Rhett Allain of dot physics, www.wired.com/wiredscience/2012/10/what-is-the-speed-of-sound/

Dan MacIsaac, Column Editor

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 574

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Abstract Unavailable
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01.50.-i Educational aids

Physics of Music and Acoustics at University of New South Wales, www.phys.unsw.edu.au/music/www.acs.psu.edu/drussell/demos.html

Dan MacIsaac, Column Editor

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 574

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Abstract Unavailable
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01.30.-y Physics literature and publications
01.40.Di Course design and evaluation
01.40.gb Teaching methods and strategies
43.75.-z Music and musical instruments
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Higgs: The Invention & Discovery of the “God” Particle: Steven Weinberg, Jim Baggott

John L. Hubisz, Reviewer

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 575

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Abstract Unavailable
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01.30.Vv Book reviews
01.50.-i Educational aids

MicroReview by the Book Review Editor: Radioactivity: A Very Short Introduction: Claudio Tuniz

John L. Hubisz, Column Editor

The Physics Teacher -- December 2012 -- Volume 50, Issue 9, pp. 575

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01.30.Vv Book reviews
23.00.00 Radioactive decay and in-beam spectroscopy
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